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Hoover Dam and Hydroelectric Power

Since its completion, Hoover Dam has wowed visitors with its sheer massiveness and its ability to create and hold back a reservoir that covers nearly 650 square kilometers (250 square miles). Yet, perhaps even more impressive is the dam's ability to harness the potential energy stored in the reservoir and convert it to electricity. In this video segment, adapted from Building Big, series host David Macaulay explores Hoover Dam's hydroelectric capabilities.

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Hoover Dam, with its elegantly arching shape and smooth, towering wallsrepresents an idea even bigger than itself. The dam symbolizes humaningenuity and our ability to transform the environment and make evena harsh desert habitable. By generating power, controlling downstreamflooding, and storing water for irrigation and municipal use, HooverDam fueled the growth of the American Southwest.

Lake Mead, the reservoir Hoover Dam creates by holding back the ColoradoRiver, holds 35 billion cubic meters (46 billion cubic yards) of water,which generates tremendous force. The water pressure near the base ofthe dam is close to 220,000 kilograms per square meter (45,000 poundsper square foot). The dam resists this force -- otherwise it wouldn'tremain standing. It also harnesses this force and uses it to generateelectricity.

Hoover Dam doesn't stand as an impenetrablebarrier to the water in the reservoir. It constantly releases water at arate of about 15,000 cubic meters (20,000 cubic yards) each second, which ismore than half the water in an Olympic-sized swimming pool. Inside thedam are 17 hydroelectric generators, each attached to a huge fan-likestructure called a turbine. As water is released from the reservoir,it flows through pipes in the dam and past the turbine blades, causingthe turbines to spin and the generators to which they're attached to turn.

Generators, including those in Hoover Dam, produceelectricity through a process called electromagnetic induction. When aloop of wire moves through a magnetic field, or vice versa, an electricalcurrent is produced. As the turbines in Hoover Dam spin, they causeelectromagnets to turn inside stationary wire loops, inducing currentin those loops.

Hoover Dam generates more than 4 billionkilowatt-hours of electricity each year, enough to serve 1.3 millionpeople. Still, this efficient and seemingly cheap source of power is notwithout its costs. Dams create impenetrable barriers to spawning fish,and large reservoirs destroy important and uncommon river and canyonwildlife habitat. They can also disrupt human habitat and submerge landthat has been traditionally available for other uses. For these reasons,environmental groups decry the existence of dams like Hoover Dam andoppose the construction of additional ones.